1. Field of the Invention
The invention relates to a clamping device for a printing cylinder for transmitting higher current volumes.
2. Description of the Prior Art
Such a clamping device is known from EP 0 596 399 A1 which is used to hold especially gravure cylinders—e.g. for printing publications—in galvanic plating. For this, the ends of the gravure cylinders are clamped between two hollow cones used as holders, oriented towards each other.
FIG. 1 shows a hollow cone described in EP 0 596 399 A1 which serves as holder 1 and is built into a galvanic plant in the manner described in EP 0 596 399 A1. Holder 1 is shown in a section in FIG. 1a), in a front view in FIG. 1b), and in a perspective view in FIG. 1c). For clarification, one axis end 2 of a printing cylinder is drawn in a broken line. FIG. 1a) clearly shows that current from holder 1 can be transmitted exclusively over an edge 3 of a front face of the axis end 2 because a contact exists only there. The high current required for electroplating is then transmitted via the hollow cones (holder 1) and the edges 3 contacting them on the front faces of the axis ends 2 into the printing cylinder. With an end diameter of approx. 100 mm and an essentially uniform distribution of current over the left and the right axis end 2, it is possible to feed up to approx. 14,000 A into the printing cylinder.
For these current volumes, the solution described in EP 0 596 399 A1 proved to be excellent. However, the development of larger gravure cylinders with a larger body width and the use of galvanic baths with higher immersion degrees of up to 100% resulted in the need for transmitting yet significantly higher currents—especially for chrome-plating—into the gravure cylinders to obtain economic processing times.
With such high current volumes, however, there is a risk of overheating of the hollow cones holding the axis ends which may result, at its worst, in burn marks on the hardened surface of the hollow steel cone, in melting insulating bushes, and in electric arcs.
The clamping device described in DE 101 21 937 A1 also does not enable the transmission of higher currents than so far.
DE 10 2004 033 332 A1 shows another clamping device in which the hollow cones have an inside contour with three holding surfaces offset from each other on which the respectively allocated end of the printing cylinder is held upon clamping. The three holding surfaces offset from each other present a kind of tripod from which the allocated axis end can be clamped in, similar to the way of a three-jaw chuck.